1. Field of the Invention
This invention relates to coatings on a substrate, and, more specifically, to coatings that do not delaminate from the substrate and to coatings that are capable of receiving indicia.
2. Description of the Related Art
It is generally known in the art that the surface properties of shaped articles such as polymeric films and fibers can be modified by graft polymerization processes wherein the article is treated with a free radical generating agent such as an organic peroxide or high energy radiation and then contacted with an ethylenically unsaturated monomeric material under conditions wherein the monomer or graft polymer chain is caused to be covalently bonded to the substrate.
One particular process involves the treatment of natural or synthetic polymer substrates containing active hydrogen with an aqueous solution containing a silver salt (silver nitrate), a free radical polymerization catalyst and a free radically polymerizable monomer. The silver salt acts upon the substrate to remove active hydrogen thereby creating active sites or free radicals along the molecular chain and initiating and propagating polymerization of the monomer in conjunction with the free radical polymerization catalyst. The resulting product is a graft copolymer comprising a substrate having a plurality of polymeric side chains covalently bonded thereto. Examples of such processes are disclosed in U.S. Pat. Nos. 3,401,049 and 3,698,931, which are incorporated herein by reference in their entireties. This process is similar to grafting processes disclosed in U.S. Pat. Nos. 5,342,659; 5,439,969; 5,552,472; and 5,741,548, which are incorporated herein by reference in their entireties.
Organic solvent-based coating compositions are known in the art based on compositions curable by condensation reactions and containing polymeric material such as hydroxy terminated polyesters, diesters, acrylics and alkyds and an amino or polyisocyanate crosslinking agent. These formulations are adapted to be applied to a substrate such as metal, heated to drive off the solvent and further heated at temperatures above 80 degrees C. to activate the crosslinking mechanism.
It is known in the prior art that it is difficult to bond ink to certain substrates such as wood-based products and plastics, and even more specifically to polyolefin. The prior art discloses that the substrates may be precoated with a material to which the ink bonds. However, the prior art also discloses that the coatings may delaminate or be otherwise removed from the substrate. This is especially true for plastic substrates that are flexible or heat shrinkable, such as polyolefin tubing.
It is known in the prior art that a substrate may be treated to grow a polymer coating using a process known as chemical grafting. The resulting coating is covalently bonded to the substrate that is resistant to delamination. Chemical grafting involves the activation of the substrate. Once the substrate has been activated, chains of monomers linked by carbon-carbon bonds grow on the substrate as whiskers. These whiskers impart new and desirable properties to the substrate without damaging any of the existing positive characteristics of the substrate.
The chemical grafting processes relics on the fact that many materials, both naturally occurring and synthetic, possess hydrogens which are more active than the xe2x80x9cbulk hydrogens.xe2x80x9d Examples of relatively more active hydrogens include the tertiary hydrogen in polypropylene, the amide hydrogen in proteins, and the hydroxyl hydrogen in polysaccharide.
The chemical grafting process utilizes graft initiators (GI) that have the capacity of removing the active hydrogens and initiating the growth of polymer chains at the site of the removed hydrogen. In the case of polypropylene, the series of reactions is represented as follows: 
A xe2x80xa2 represents a free radical, anion or cation, depending on whether the GI removes a hydrogen and one electron, no electrons, or two electrons. The below structure: 
represents a unit of vinyl monomer where X governs the property or properties that are obtained with the resulting polymers attached and grown on the substrate. The graft polymer chains are formed from vinyl monomers or monomers containing appropriate functionability, e.g. groups such as hydroxyl, carboxyl, epoxy, amide, amine anhydride. In many instances a mixture of monomers is employed and often more than one property can be altered in one processing step. The polymers, whose length can be controlled, are permanently attached to the substrate. The linkage is between the grafted polymer and the substrate is covalent and cannot be leached or otherwise removed from the substrate absent mechanical means such as abrasion.
In an aspect of the invention, a composition provides a chemically grafted coating onto a substrate, wherein the composition comprises an acrylate and a grafting initiator. In further aspects of the invention, the acrylate is a waterborne urethane acrylate.
In further aspects of the invention, the composition comprises resistance agent, an adhesion agent, a UV curing photoinitiator, a defoaming agent, and/or a deglossing agent. The resistance agent increases the chemical or mechanical resistance of the coating. In still further aspects of the invention, the resistance agent is an acryl-alkyd emulsion, a polyether, or a polyethylene glycol diacrylate. In other aspects of the invention, the adhesion agent is a polyethylene glycol diacrylate or an ethoxylated trimethylol propane triacrylate monomer. In additional aspects of the invention, the UV curing photoinitiator is 2-hydroxy-2-methyl-1 phenyl-propane-1 -one.
In an aspect of the invention, the composition comprises VIAKTIN VTE 6155W/50WA at 20-30 parts per weight; RESYDROL VAY 6278W/45WA at 4-5 parts per weight; RESYDROL AY 586 W/28 WA at 5-7 parts per weight; BYK 024 at 0.1-0.2 parts per weight; FUJI 370 at 1.5-3.0 parts per weight; SR 344 at 0.12-0.20 parts per weight; de-ionized water at 4-50 parts per weight; ferrous ammonium sulfate (0.1% in deionized water) at 0.10-0.15 parts per weight; and DARACUR 1173 at 1.2-1.8 parts per weight.
In as aspect of the invention, the composition comprises VIAKTIN VTE 6155W/50WA at approximately 28.95 parts per weight; RESYDROL VAY 6278W/45WA at approximately 4.45 parts per weight; RESYDROL AY 586 W/28 WA at approximately 5.00 parts per weight; BYK 024 at approximately 0.10 parts per weight; FUJI 370 at approximately 1.8 parts per weight; SR 344 at approximately 0.16 parts per weight; de-ionized water at approximately 46.00 parts per weight; ferrous ammonium sulfate (0.1% in de-ionized water) at approximately 0.10 parts per weight; and DARACUR 1173 at approximately 1.55 parts per weight.
In an aspect of the invention, the composition comprises VIAKTIN VTA 6155W/50WA at approximately 28.95 parts per weight; RESYDROL VAY 6278W/45WA at approximately 4.45 parts per weight; RESYDROL AY 586 W/28 WA at approximately 5.00 parts per weight; BYK 024 at approximately 0.10 parts per weight; FUJI 370 at approximately 1.40 parts per weight; SR9035 at approximately 0.20 parts per weight; de-ionized water at approximately 46.00 parts per weight; ferrous ammonium sulfate (0.1% in de-ionized water) at approximately 0.10 parts per weight; and DARACUR 1173 at approximately 1.55 parts per weight.
In an aspect of the invention, the substrate is plastic or wood. In a still further aspect of the invention, the substrate is polyolefin.
In an aspect of the invention, a process for chemically grafting a coating onto a substrate comprising the step of providing a composition comprising an urethane acrylate and a grafting initiator along with the step of coating the substrate with the composition and curing the composition coated on the substrate. Further aspects of the invention include a product made by the process and that the substrate is plastic or wood, such as polyolefin for example.
In a further aspect of the invention, the curing step further comprises curing the composition coated on the substrate under a D bulb and an H bulb at a rate of 100-160 feet/minute. In a still further aspect of the invention, a product is made by the process having the step of curing the composition under the D bulb and the H bulb at the rate of 100-160 feet/minute. In an additional aspect of the invention, the substrate is polyolefin.
In still further aspects of the invention, processes use the compositions described above and products made with these processes, including having polyolefin as a substrate.
In still further aspects of the invention, the processes include the step of applying readable indicia onto the coating. In a still further aspect of the invention, the readable indicia is ink.
In an embodiment of the invention, a co-polymer, a monomer/prepolymer and a graft initiator are mixed together and coated onto a substrate, such as plastic or wood. The resulting coating is then cured, resulting in a covalently bonded polymer coating on the substrate. In a more preferred embodiment of the invention, the substrate is flexible, such as heat shrinkable polyolefin tubing, and the copolymer comprises a functional group to add flexibility to the bonded polymer coating, with an example of such a functional group being urethane.
In embodiments of the invention, the functional groups of the monomers and prepolymers may consist of hydroxyl groups, carboxyl groups, secondary and/or tertiary amino groups, and epoxy groups. In a preferred embodiment of the invention, the molecular ratio of the reactive components of the mixture are adjusted so that no free groups are left after the reaction is complete. Examples of suitable monomers include ethoxylated trimethyl propane triacrylate, polyethylene glycol (400) diacrylate, sodium vinyl sulfate, ethoxylated bisphenol A dimethacrylate, ethoxylated bisphenol A diacrylate, trifunctional methacrylate ester, trifunctional acrylate ester, alkoxyated diacrylate. The concentration of the monomers in the solution can vary within practically any limits. In a preferred embodiment of the invention, the concentration of monomers is between about 0.1% and about 50% of the formulation and, more preferably, between about 0.1% and about 20%.
In a step of the reaction, one of the terminal hydrogens of the co-polymer is covalently bonded to the substrate. This is accomplished by the graft initiator acting as a catalyst. The graft initiator in a preferred embodiment of the invention is ferrous ammonium sulfate which contributes the metal ion Fe++. Other embodiments of the invention may use graft initiators that contribute any other suitable metal ion, such as Fe+++, Ag+, Co++, Cu++, and ions of cerium for example. The choice of the metal ion depends of the nature of the substrate. In a preferred embodiment of the invention, only a single ion is used as a graft initiator and not a combination of ions. In a preferred embodiment of the invention the graft initiator ion salt concentration may vary in the rage of about 0.01% to 0.1% by weight of the monomers.
In an embodiment of the invention, the copolymer comprises ethylene vinyl acetate copolymer (EVA) and/or ethylene ethyl acrylate copolymer (EEA), represented as structures (3) and (4), respectively, below. 
The EVA and/or and the EEA is grafted to the substrate and is represented as xe2x80x9cR-Hxe2x80x9d in the below structures and reactions. The mechanism of reaction between the EVA and/or the EEA and the monomer/prepolymer is carried out via a free radical mechanism as disclosed below.
In the first stage of the free radical mechanism, the substrate reacts with the graft initiator (GI) to create the radical: 
The propagation of the polymer is then initiated by a monomer bonding to the radical: 
and the polymer propagating therefrom and terminating chain propagation as shown in steps (7) and (8): 
xe2x80x9cXxe2x80x9d represents side functional groups, which may react between themselves and with additional prepolymers or polymers included in the mixture. The reaction of the side functional groups may result in the polymer coating being crosslinked.
A radical combination reaction is used to terminate the polymer propagation step. In a preferred embodiment of the invention, the radical combination reaction is initiated by a UV curing step. Other embodiments of the invention may have the free radical produced by any other suitable means, such as by supplying a peroxide. The peroxide supplier may be any suitable catalyst, such as benzoyl peroxide, methyl ethyl ketone peroxide, tert butyl hydroperoxide, hydrogen peroxide, and ammonium ferrous sulfate. In an embodiment of the invention, the concentration of the catalyst may vary in the range of about 0.1% to about 5.0% of the polymerization solution and, in a preferred embodiment of the invention, between about 0.1% and about 10%.
In embodiments of the invention, the mixture coating may be applied to the substrate using any suitable method, such a brushing, spraying, and dipping. Embodiments of the invention have mixtures of appropriate properties for the specific application method. For example, a low viscosity mixture may be used for a spraying application.
In a preferred embodiment of the invention, ink or another indicia creating substance is applied to the coating, either before or after curing, to dispose readable indicia on the coating surface. The indicia creating substance may be visible or invisible. The invisible indicia creating substance may be, for example, machine readable, comprise electrically charged or magnetically charged particles, emit electromagnetic wavelengths outside of the visible light wavelength band, or any other suitable application.